Arenaviruses are rodent-borne viruses that cause hemorrhagic fevers in Latin America and West Africa, and are considered potential bioterrorism threats. The long-term goal of my laboratory is to elucidate mechanisms of arenavirus pathogenicity. Human studies have suggested that pro-inflammatory cytokines are important in disease outcome, but existing data conflict as to whether they play a protective or pathogenic role. This issue is most readily addressed using a small animal model, such as the Pichinde virus (PIC) model in use in our lab. The model utilizes a PIC variant (P18) which has been "adapted" by serial guinea pig passages to cause a severe, Lassa fever-like disease in guinea pigs. A corresponding, low passage variant (P2) is naturally attenuated and causes a self-limited febrile illness. This pair of variants affords a comparative approach to understanding the role of cytokines in arenavirus disease. Like other arenaviruses, both PIC variants are macrophage-tropic. Macrophage-derived cytokines are important effectors in the terminal pathophysiology of septic shock and other viral hemorrhagic fevers, and some have direct anti-viral effects in cultured cells. Therefore, the central hypothesis of the proposed research is that specific patterns of cytokine induction from macrophages determine arenavirus pathogenicity. This hypothesis will be addressed in the following specific aims. Aim 1: To compare local and systemic cytokine expression patterns during guinea pig experimental infection with PIC variants using real-time RT-PCR (for TNF alpha, IL-1, IL-12rho40, IL-10, GRO, IL-8, RANTES,TGF-beta, bioassay (for TNF alpha, IL-6) and ELISA (for IL-8, TGF- alpha. Aim 2: To compare patterns of monokine expression during infection of primary guinea pig macrophages with PIC variants, and correlate with any observable differences in viral replication. Aim 3: To determine the effects of specific cytokines (including TNF alpha, IFN gamma, IL-8) on PIC replication in primary guinea pig macrophage system. These experiments will represent the first systematic characterization of cytokine responses to a viral hemorrhagic fever in a guinea pig model. Results from the proposed studies will have important implications for future research in arenavirus hemorrhagic fevers, including BL-4 agents.